U.S. patent application number 15/763301 was filed with the patent office on 2019-02-28 for surface property measurement method, surface property measurement apparatus, and recording medium.
This patent application is currently assigned to SHISEIDO COMPANY, LTD.. The applicant listed for this patent is HONDA ELECTRONICS CO., LTD., NATIONAL UNIVERSITY CORPORATION TOYOHASHI UNIVERSITY OF TECHNOLOGY, SHISEIDO COMPANY, LTD.. Invention is credited to Yusuke HARA, Naohiro HOZUMI, Kazuto KOBAYASHI, Yuki OGURA, Sachiko YOSHIDA.
Application Number | 20190059857 15/763301 |
Document ID | / |
Family ID | 58493476 |
Filed Date | 2019-02-28 |
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United States Patent
Application |
20190059857 |
Kind Code |
A1 |
OGURA; Yuki ; et
al. |
February 28, 2019 |
SURFACE PROPERTY MEASUREMENT METHOD, SURFACE PROPERTY MEASUREMENT
APPARATUS, AND RECORDING MEDIUM
Abstract
A surface property measurement technology by which a surface
property of a substance can be evaluated with high accuracy, is
provided. A surface property measurement method includes radiating
an ultrasonic wave to a measurement target and acquiring a
reflected signal from the measurement target; calculating, by a
measurement apparatus, a maximum value of a cross-correlation
function between the reflected signal from the measurement target
and a reference reflected signal from a reference substance
acquired in advance; calculating a reflection component at an
interface, by using the maximum value of the cross-correlation
function; and outputting, as a measurement value, one of an
acoustic impedance of the measurement target or an acoustic
impedance of the reference substance, according to a result of
comparing the reflection component with the reference reflected
signal.
Inventors: |
OGURA; Yuki; (Kanagawa,
JP) ; HOZUMI; Naohiro; (Aichi, JP) ; YOSHIDA;
Sachiko; (Aichi, JP) ; KOBAYASHI; Kazuto;
(Aichi, JP) ; HARA; Yusuke; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHISEIDO COMPANY, LTD.
NATIONAL UNIVERSITY CORPORATION TOYOHASHI UNIVERSITY OF
TECHNOLOGY
HONDA ELECTRONICS CO., LTD. |
Tokyo
Aichi
Aichi |
|
JP
JP
JP |
|
|
Assignee: |
SHISEIDO COMPANY, LTD.
Tokyo
JP
NATIONAL UNIVERSITY CORPORATION TOYOHASHI UNIVERSITY OF
TECHNOLOGY
Aichi
JP
HONDA ELECTRONICS CO., LTD.
Aichi
JP
|
Family ID: |
58493476 |
Appl. No.: |
15/763301 |
Filed: |
September 13, 2016 |
PCT Filed: |
September 13, 2016 |
PCT NO: |
PCT/JP2016/076973 |
371 Date: |
March 26, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 8/5238 20130101;
G01N 2291/015 20130101; G01N 29/50 20130101; A61B 8/587 20130101;
G01N 29/46 20130101; G01N 2291/044 20130101; A61B 8/0858 20130101;
G01N 29/041 20130101; A61B 8/4427 20130101; G01N 29/09 20130101;
G01N 29/11 20130101; G01N 29/4436 20130101; A61B 8/485
20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; G01N 29/09 20060101 G01N029/09; G01N 29/04 20060101
G01N029/04; G01N 29/50 20060101 G01N029/50; A61B 8/00 20060101
A61B008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2015 |
JP |
2015-192075 |
Sep 8, 2016 |
JP |
2016-175317 |
Claims
1. A surface property measurement method comprising: radiating an
ultrasonic wave to a measurement target and acquiring a reflected
signal from the measurement target; calculating, by a measurement
apparatus, a maximum value of a cross-correlation function between
the reflected signal from the measurement target and a reference
reflected signal from a reference substance acquired in advance;
calculating a reflection component at an interface, by using the
maximum value of the cross-correlation function; and outputting, as
a measurement value, one of an acoustic impedance of the
measurement target or an acoustic impedance of the reference
substance, according to a result of comparing the reflection
component with the reference reflected signal.
2. The surface property measurement method according to claim 1,
further comprising: calculating and outputting the acoustic
impedance of the measurement target, upon determining that an
intensity of the reflection component is lower than an intensity of
the reference reflected signal.
3. The surface property measurement method according to claim 1,
further comprising: outputting the acoustic impedance of the
reference substance, upon determining that an intensity of the
reflection component is not lower than an intensity of the
reference reflected signal.
4. The surface property measurement method according to claim 1,
wherein the calculating of the reflection component includes
multiplying the reference reflected signal by a ratio of the
reflected signal from the measurement target to the reference
reflected signal and by the maximum value of the cross-correlation
function.
5. The surface property measurement method according to claim 1,
further comprising: one-dimensionally or two-dimensionally and
relatively scanning the ultrasonic wave to the measurement target;
and outputting the measurement value for each coordinate point.
6. The surface property measurement method according to claim 1,
wherein the radiating of the ultrasonic wave includes radiating the
ultrasonic wave upon bringing an acoustic window of a probe of the
measurement apparatus in contact with the measurement target.
7. The surface property measurement method according to claim 1,
wherein the reference substance is water or a gelatinous
substance.
8. The surface property measurement method according to claim 1,
wherein the measurement target is skin, and wherein the surface
property measurement method further comprises: evaluating at least
one of elasticity, texture, pores, and wrinkles of the skin, based
on the measurement value.
9. The surface property measurement method according to claim 1,
wherein the measurement target is an organic or inorganic,
single-layered or multilayered substance, and wherein the surface
property measurement method further comprises: evaluating at least
one of surface roughness, elasticity, and defects of an outermost
layer of the measurement target, based on the measurement
value.
10. A non-transitory computer-readable recording medium storing a
surface property measurement program that causes a computer to
execute a process, the process comprising: acquiring a reflected
signal of an ultrasonic wave radiated to a measurement target;
calculating a maximum value of a cross-correlation function between
the reflected signal from the measurement target and a reference
reflected signal from a reference substance acquired in advance;
calculating a reflection component at an interface, by using the
maximum value of the cross-correlation function; and outputting, as
a measurement value, one of an acoustic impedance of the
measurement target or an acoustic impedance of the reference
substance, according to a result of comparing the reflection
component with the reference reflected signal.
11. A surface property measurement apparatus comprising: an
ultrasonic wave transmitting/receiving unit configured to radiate
an ultrasonic wave to a measurement target and receive a reflected
signal from the measurement target; a memory configured to store an
intensity of a reference reflected signal from a reference
substance measured in advance, and an acoustic impedance of the
reference substance; and a signal processing unit configured to
calculate a reflection component at an interface, based on a
maximum value of a cross-correlation function between the reflected
signal from the measurement target and the reference reflected
signal, and output, as a measurement value, one of an acoustic
impedance of the measurement target or the acoustic impedance of
the reference substance, according to a result of comparing the
reflection component with the reference reflected signal.
12. The surface property measurement apparatus according to claim
11, wherein the signal processing unit calculates and outputs the
acoustic impedance of the measurement target, upon determining that
an intensity of the reflection component is lower than the
intensity of the reference reflected signal.
13. The surface property measurement apparatus according to claim
11, wherein the signal processing unit reads, from the memory, and
outputs the acoustic impedance of the reference substance, upon
determining that an intensity of the reflection component is not
lower than the intensity of the reference reflected signal.
Description
TECHNICAL FIELD
[0001] The present invention relates to measurement of surface
properties, and in particular, to measurement of physical
properties of a surface and/or surface layer of an object by using
ultrasonic waves.
BACKGROUND ART
[0002] Evaluation of the properties of a surface and/or surface
layer of an object is useful in various fields. For example, in the
case of a living body, the skin exists on the surface and/or
surface layer of the living body, and by recognizing the skin
quality that is a property of the skin, it is possible to perform
skin care according to the skin quality and maintain healthy skin.
In the field of beauty and cosmetics, the skin quality is generally
evaluated according to inquiries by a beauty technician, etc.
Furthermore, dynamic properties of the skin (skin flexibility and
elasticity, etc.) and optical properties of the skin (skin luster
and transparency, etc.) have been measured by using measuring
instruments, and skin conditions and functions have been
objectively evaluated.
[0003] Conventional methods of measuring the physical properties of
skin by using a noninvasive measuring instrument, are generally
performed by applying stress on the surface of the skin under
constant conditions, and by measuring the reaction force or
response after applying constant displacement. The values obtained
by these measurement methods have been detected as evaluation
values of physical properties of the entire skin. However, the
property value is detected as a value including all contributions
of the respective layers constituting the skin (horny cell layer,
epidermis, dermis, and subcutaneous tissue). Since each layer
constituting the skin has its own role and function, it is
desirable that each layer can be individually measured and
evaluated.
[0004] In particular, the horny cell layer at the outermost layer
of the skin has a barrier function and a moisturizing function
necessary for maintaining life activities, and therefore accurate
measurement of property values of the horny cell layer is an
important task in the medical and pharmaceutical fields.
Furthermore, the object that can be appealed in skin care is
limited to the horny cell layer in terms of pharmaceutical affairs,
and therefore the property evaluation of only the horny cell layer
is also meaningful in the field of beauty and cosmetics. However,
by the conventional stress/displacement application type
noninvasive skin measuring instrument, it has been impossible to
measure the physical properties of only the horny cell layer. In
order to measure the physical property value of each layer of the
skin, it has been necessary to use an invasive technique using a
cut skin piece of a biopsy, etc., instead of the noninvasive
technique. For example, the method of Patent Literature 1 is a
method of measuring a sound velocity distribution of a skin
cross-section by preparing a tomographic sample of the skin. By
this method, it is possible to measure the hardness of each region
of the skin by the sound velocity of each layer of the skin
tomography, that is, the physical property value that is an index
of the volume elasticity.
[0005] FIG. 1 is a sound velocity distribution image of a
cross-section of a skin piece cut by a conventional method. Image
(A) of FIG. 1 illustrates a skin piece of the cheek of a young
person, and an image (B) of FIG. 1 illustrates a cross-section of a
skin piece of the cheek of an elderly person. As illustrated in
FIG. 1, it is known that complex variations can be observed;
specifically, in the skin (cheek) exposed to ultraviolet rays, the
sound velocity in the horny cell layer at the outermost layer is
high (hard), while the sound velocity, that is, the volume
elasticity in the middle layer of the dermis decreases (softens).
With regard to the measurement target in which such complex
variations are observed, it is impossible to evaluate the physical
properties of only the surface and/or surface layer, by
conventional noninvasive skin measuring instruments of the
stress/displacement application type. By actually evaluating the
skin (cheek) exposed to ultraviolet rays, with a skin
viscoelasticity measuring device by the suction method (a method of
evaluating the height of the skin floating up when the skin is
depressurized with constant pressure), which is widely used as a
noninvasive skin measuring instrument, the influence of the
softening of the dermis is applied largely to the evaluation
results, and it is not possible to capture the phenomenon of the
surface and/or surface layer becoming hard.
[0006] Note that other than conventional noninvasive skin measuring
instruments based on stress/displacement application, in recent
years, there has been proposed a technique for noninvasively
obtaining hardness information at different depths of the skin, by
using ultrasonic waves (Patent Literature 2). In this method,
information of a plurality of layers at different depths is
measured by radiating ultrasonic waves including different
frequency components to the skin, and calculating the acoustic
impedance of the reflected waves. It is possible to distinguish
between the information from the inside of the skin and the
information of the skin surface and/or surface layer, and it is
possible to obtain physical properties only of the skin surface
and/or surface layer.
CITATION LIST
Patent Literature
[0007] [PTL 1] [0008] Japanese Unexamined Patent Application
Publication No. 2007-271765 [0009] [PTL 2] [0010] Japanese
Unexamined Patent Application Publication No. 2006-271765
SUMMARY OF INVENTION
Technical Problem
[0011] In the technique of Patent Literature 2 described above,
information of each layer constituting the skin is acquired by
pressing the leading end of a probe against the skin, receiving
reflected waves of different frequencies from the skin, and
measuring the reflected waves.
[0012] However, this technique does not consider the influence of
fine irregularities existing on the skin surface (skin grooves and
skin hillocks). Actually, even when the leading end of the probe is
pressed against the skin, the portions of the skin grooves can
hardly come into contact with the leading end surface of the probe,
and at the portions that are not in contact, it is not possible to
accurately acquire the acoustic impedance of the horny cell layer.
This problem is not limited to the measurement of skin, but also
applies to the measurement of the surface of a living body such as
a tooth or a nail, or the measurement of an organic or inorganic
surface and/or surface layer in which fine irregularities
exist.
[0013] In view of the above, it is an object of the present
invention to provide a technique and a configuration for surface
property measurement by which the surface properties of a substance
can be accurately evaluated.
Solution to Problem
[0014] In order to solve the above-described problem, a reflection
component is extracted at the maximum point in a cross-correlation
function between a reflected waveform from a measurement target and
a reference waveform that is a reflected waveform from a reference
substance (specifically, an ultrasonic transmission medium or pure
water used as a couplant), and an acoustic impedance representing
the surface property is calculated according to a result of
comparing the reflection component with the reference waveform.
[0015] Specifically, a surface property measurement method
includes
[0016] radiating an ultrasonic wave to a measurement target and
acquiring a reflected signal from the measurement target;
[0017] calculating, by a measurement apparatus, a maximum value of
a cross-correlation function between the reflected signal from the
measurement target and a reference reflected signal from a
reference substance acquired in advance;
[0018] calculating a reflection component at an interface, by using
the maximum value of the cross-correlation function; and
[0019] outputting, as a measurement value, one of an acoustic
impedance of the measurement target or an acoustic impedance of the
reference substance, according to a result of comparing the
reflection component with the reference reflected signal.
Advantageous Effects of Invention
[0020] According to the above technique, a surface property of a
substance can be evaluated with high accuracy.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a hardness distribution image of a cross-section
of skin measured by a known method (method of Patent Literature
1);
[0022] FIG. 2 is a schematic diagram of a surface property
measurement apparatus according to an embodiment;
[0023] FIG. 3 is a block diagram of the surface property
measurement apparatus of FIG. 2;
[0024] FIG. 4 is a diagram illustrating a reflection state of
ultrasonic waves;
[0025] FIG. 5 is a diagram for describing the principle of the
embodiment;
[0026] FIG. 6 is a diagram for describing a cross-correlation
between a reflected waveform from a measurement target and a
reference waveform;
[0027] FIG. 7 is a flowchart of the surface property measurement
method according to the embodiment;
[0028] FIG. 8 illustrates a measurement result when the
cross-correlation between the reflected wave from the target and
the reference wave is not used;
[0029] FIG. 9 illustrates a measurement result when the
cross-correlation between the reflected wave from the target and
the reference wave is used;
[0030] FIG. 10 illustrates a process flow when a measurement result
is displayed as an image;
[0031] FIG. 11A is an image illustrating the state of the skin
surface actually measured by using the surface property measurement
apparatus according to the embodiment;
[0032] FIG. 11B is an image illustrating the state of the skin
surface actually measured by using the surface property measurement
apparatus according to the embodiment;
[0033] FIG. 11C is an image illustrating the state of the skin
surface actually measured by using the surface property measurement
apparatus according to the embodiment;
[0034] FIG. 11D is an image illustrating the state of the skin
surface actually measured by using the surface property measurement
apparatus according to the embodiment; and
[0035] FIG. 12 illustrates the average acoustic impedance by age
based on the measurement data of FIGS. 11A to 11D.
DESCRIPTION OF EMBODIMENTS
[0036] Hereinafter, embodiments of the present invention will be
described with reference to the drawings.
[0037] FIG. 2 is a schematic diagram of a surface property
measurement apparatus 1 according to an embodiment. The surface
property measurement apparatus 1 includes a probe 2 and an
information processing apparatus 3. The probe 2 includes an
acoustic window 5 at the leading end, through which ultrasonic
waves can pass. The material of the acoustic window 5 that contacts
the measurement target has a known acoustic impedance that differs
from that of the measurement target, and is formed of a hard
material (for example, hard resin, etc.) capable of passing
ultrasonic waves.
[0038] The probe 2 can communicate with the information processing
apparatus 3. In the example of FIG. 2, the probe 2 is connected by
a cable 4; however, the probe 2 may be wirelessly connected. From
the acoustic window 5 of the probe 2, ultrasonic waves that are
two-dimensionally scanned and transmitted, are radiated to the
measurement target, the reflected waves are received by the probe 2
and converted into electric signals, and the electric signals are
output. The received reflected waves include information on the
measurement target.
[0039] The probe 2 can be grasped by hand; for example, when
measuring the skin, the probe 2 can be held by hand and directly
applied to the subject's skin. Furthermore, when highly accurate
measurement is desired without being affected by movement of the
body, it is also possible to fix the probe 2 or fix the probe 2 and
the cheek of a person together with double-sided tape.
[0040] The information processing apparatus 3 analyzes the
reflected waves received by the probe 2 and detects the surface
properties of the measurement target. As the information processing
apparatus 3, any information processing apparatus having an
arithmetic processing function and a display function can be used,
such as a notebook computer and a tablet terminal, etc. In the
embodiment, the information processing apparatus 3 obtains the
maximum cross-correlation between the reflected waveform from the
measurement target and a reference waveform, to remove the
interference with the reflected waveform from internal components
of the measurement target and the influence of irregularities of
the surface shape (influence on the reflected waveform due to
contact and non-contact with the acoustic window), and extract an
accurate acoustic impedance of the surface and/or surface layer.
For example, when the measurement target is skin, the accurate
physical property information such as the hardness and the
elasticity of the skin surface layer (horny cell layer) is
acquired, upon excluding the interference from the epidermis and
dermis in the skin and the influence of irregularities of the
surface shape (texture and wrinkles, etc.). When the measurement
target is a tooth, information such as the accurate hardness of
enamel of the surface is measured, upon excluding the influence of
the internal cementum and dentin and the influence of
irregularities of the surface shape (roughness). When the
measurement target is a multilayer film or a multilayer coating
material, information such as the hardness and elasticity of the
outermost layer is measured, upon reducing the influence of the
inner layers and the influence of the irregularities of the surface
shape.
[0041] FIG. 3 is a block diagram of the surface property
measurement apparatus 1 of FIG. 2. The probe 2 includes an
ultrasonic sensor circuit 21 and an interface (I/F) 27. The
interface 27 may be a wireless interface or a physical interface as
described above.
[0042] The ultrasonic sensor circuit 21 includes a transmitting
unit 22, a receiving unit 24, a transmission/reception separation
circuit 25 that separates transmission waves and reception waves,
and a transducer 28. The transmitting unit 22 includes a pulse
generation circuit 23. The pulse generation circuit 23 generates a
drive pulse at a predetermined timing. The transmitting unit 22
applies the drive pulse to the transducer 28 via the
transmission/reception separation circuit 25. The transducer 28
converts the pulse (electric) signals into mechanical vibration and
outputs ultrasonic waves.
[0043] The transducer 28 receives the reflected wave reflected from
the measurement target and converts the reflected wave into an
electric signal. The reception electric signal is supplied to the
receiving unit 24 by the transmission/reception separation circuit
25. The receiving unit 24 detects an analog electric signal and
converts the analog electric signal into a digital signal by an
analog/digital converter (ADC). The digital signal (reflected wave)
is transmitted to the information processing apparatus 3 via the
interface 27.
[0044] The information processing apparatus 3 includes a CPU 31, an
interface (I/F) 32, a memory 33, a DSP (Digital Signal Processor)
34, an input device 35, a display device 36, and a storage device
37. The reflected wave signal transmitted from the probe 2 is input
to the DSP 34 via the interface 32, and the reflected wave signal
is processed by the DSP 34.
[0045] The input device 35 is an input user interface such as a
touch panel, a mouse, and a keyboard, etc. The display device 36 is
a monitor display such as a liquid crystal display, a plasma
display, and an organic EL (electroluminescence) display, etc. The
storage device 37 is a hard disk drive such as a magnetic disk
device or an optical disk device, and stores various programs and
data. The memory 33 includes a RAM (Random Access Memory) and a ROM
(Read-Only Memory), and stores the reflected waveform of the
reference substance and the acoustic impedance thereof that are
acquired in advance for ultrasonic measurement.
[0046] The DSP 34 determines the surface properties from the
acoustic impedance of the measurement target based on the maximum
cross-correlation between the reflected waveform from the
measurement target and the reflected waveform from a reference
substance. In the embodiment, it is assumed that the DSP 34
processes the signals of reflected ultrasonic waves. However, when
using a surface property measurement program to be described later,
the CPU 31 may read out the surface property measurement program
stored in the storage device 37 and execute signal analysis.
[0047] FIG. 4 is a diagram illustrating a reflection state of
ultrasonic waves. For example, a case of measuring a horny cell
layer 51 on the skin surface is considered. The skin is formed of
epidermis 52, dermis 53, subcutaneous tissue (not illustrated), and
multiple layers. The outermost surface of the epidermis 52 is the
horny cell layer 51. On the surface of the skin, there are fine
irregularities, that is, skin grooves 55 and skin hillocks 56. The
skin grooves 55 are grooves that partition the surface of the skin
into the fine skin hillocks 56; the portions of wrinkles and pores
where the skin grooves are deep and roughened are also included in
the skin grooves 55. Even when the acoustic window 5 of the probe 2
is pressed against the skin, in reality, the skin grooves 55 are
not in contact with the acoustic window 5. Between the acoustic
window 5 and the skin grooves 55, there is a couplant (ultrasonic
coupling medium) 10 such as water and gel. Ultrasonic waves are
almost 100% reflected in the air layer, and therefore in ultrasonic
measurement, the couplant 10 is usually provided between the
transducer 28 and the skin, to ensure the transmission of sound
energy between the transducer 28 and the skin.
[0048] In the portions of the skin grooves 55, the acoustic window
5 cannot make direct contact with the horny cell layer 51, but
contacts the couplant 10. Therefore, by the conventional method, it
has been impossible to acquire accurate acoustic impedance of the
horny cell layer 51. This is because the skin grooves 55 that
actually exist on the skin, are treated as the skin hillocks 56. In
the case of measuring the surface properties of a measurement
target having fine irregularities, it is necessary to make
evaluations upon distinguishing the acoustic impedance acquired at
protrusions (for example, the skin hillocks 56) from the acoustic
impedance acquired at the recesses (for example, the skin grooves
55).
[0049] FIG. 5 is a diagram for describing the principle of the
embodiment. In the embodiment, a reference signal representing the
reflected waveform from the couplant 10 as the reference substance,
and the acoustic impedance thereof, are acquired in advance. The
maximum cross-correlation between the reflected waveform of the
ultrasonic wave reflected by the measurement target (for example,
the skin) and the reference waveform is obtained, to remove the
reflection component from a layer deeper than the horny cell layer
51 on the surface, and extract the reflection information at the
interface with the acoustic window 5. By comparing the reflection
information with the reference signal, it is determined whether the
acoustic window 5 is in direct contact with the skin, or whether
the acoustic window 5 is contacting a portion of the skin groove 55
in which the couplant 10 has entered.
[0050] At a portion where the acoustic window 5 is in direct
contact with the horny cell layer 51, a reflected waveform st1 is
obtained. The maximum peak is a component reflected at the
interface between the horny cell layer 51 and the acoustic window
5. A plurality of small peaks appearing behind the maximum peak are
components reflected at portions deeper than the horny cell layer
51. For example, the components are reflected at an interface
between the horny cell layer 51 and the epidermis 52, an interface
between the epidermis 52 and the dermis 53 (see FIG. 4), and an
interface between the dermis 53 and the subcutaneous tissue,
etc.
[0051] On the other hand, at a portion where the acoustic window 5
does not contact the horny cell layer 51, a reflected waveform st2,
which is different from the reflected waveform st1, is obtained.
This includes the component reflected at the interface between the
acoustic window 5 and the couplant 10 and the component reflected
at the interface between the couplant 10 and the horny cell layer
51. Furthermore, similar to the reflected waveform st1, the
reflection component from a deeper portion of the skin is also
included.
[0052] In order to obtain a reference waveform of a reflected wave
from the couplant 10, the acoustic window 5 or a substrate having
the same quality and the same thickness as the acoustic window 5,
is brought into contact with only the couplant 10, and a reflected
wave from the interface between the acoustic window 5 and the
couplant 10 is acquired. This corresponds to a reference wave
sr.
[0053] FIG. 6 is a diagram for describing a cross-correlation
function. In the embodiment, the cross-correlation function between
the Fourier transform of each of the measured reflected wave and
the reference wave is calculated. In FIG. 6, as a matter of
convenience of description, the cross-correlation function by the
waveform in the time domain before the Fourier transform, will be
described.
[0054] The cross-correlation function is a value obtained by
integrating the product of the reflected wave st from the
measurement target and the reference wave sr, and then dividing the
result of integration by the product of the effective values (rms:
root-mean-square) of the waveforms, and obtaining a value from -1
to 1. Assuming that a digitally sampled waveform is a
multidimensional vector, the correlation between the reflected wave
st from the target and the reference wave sr is a value obtained by
dividing the inner product of the vectors by the product of the
absolute values. The result of calculating the correlation
coefficient while changing the time difference of the waveforms, is
the cross-correlation function.
[0055] In both the reference wave sr from the reference substance
and the reflected wave st from the target, the reflection from the
interface with the acoustic window 5 is strongest. The reflection
from a portion behind (deeper than) the interface with the acoustic
window 5, is smaller than the reflection from the interface with
the acoustic window 5. Therefore, the point at which the
cross-correlation function between the reflected wave st from the
target and the reference wave sr becomes maximum, indicates the
position of the interface with the acoustic window 5. The
cross-correlation function at this time is expressed as Rmax.
[0056] By obtaining the maximum value of the cross-correlation
function, the reflection component at a deeper part than the
interface with the acoustic window 5 is removed. Note that in the
case where the acoustic window 5 or the substrate is curved in a
protruding shape, a deviation occurs in the position of Rmax in
FIG. 7. That is, a position .DELTA.t on the time axis when the
cross-correlation function becomes maximum, will not be zero.
[0057] The reflected wave st in the time domain from the
measurement target is Fourier transformed, to calculate a reflected
signal St in the frequency domain. Furthermore, the reference wave
sr is Fourier transformed to calculate the reference signal Sr in
the frequency domain. By using these signals, the magnitude of a
reflection component St.sup.(1) at the interface when the
cross-correlation function becomes maximum, is obtained. St.sup.(1)
is calculated from equation (1).
[ Equation 1 ] ##EQU00001## S t ( 1 ) = R m | S t | | S r | S r ( 1
) ##EQU00001.2##
[0058] Here, Rm is the maximum value of the cross-correlation
function between the Fourier-transformed reflected signal St and
the reference signal Sr, |St| is the absolute value of the
reflected signal St, and |Sr| is the absolute value of the
reference signal Sr.
[0059] As described above, St.sup.(1) is the reflection intensity
at the interface where the acoustic window 5 directly contacts the
substance. If the magnitudes of St.sup.(1) and Sr are equal, the
couplant 10 directly contacts the acoustic window 5, and it can be
determined that this contact portion corresponds to the portion of
the skin groove 55. In this case, the acoustic impedance of the
reference substance (the couplant 10) acquired in advance, is
output. Note that in the present specification and claims, when the
magnitudes of the reflected signal and the reference signal are
"equal", it is assumed that slight errors are included due to
variations in the materials of the couplant and the acoustic
window, and variations in measurement conditions, etc.
[0060] When St.sup.(1) is lower than Sr (St.sup.(1)<Sr), the
acoustic impedance of the substance directly contacting the
acoustic window 5 is higher than the acoustic impedance of the
couplant 10 that is the reference substance, and therefore it can
be determined that the acoustic window 5 is contacting the horny
cell layer 51. In this case, the acoustic impedance of the horny
cell layer 51 is calculated from the equation (2).
[ Equation 2 ] ##EQU00002## Z t = 1 - S t S r Z s - Z r Z s + Z r 1
+ S t S r Z s - Z r Z s + Z r Z s ( 2 ) ##EQU00002.2##
[0061] Here, Zt is the acoustic impedance of horny (skin) in
contact with the acoustic window 5 (or an ultrasonic radiation
window), Zs is the acoustic impedance of the acoustic window, Zr is
the acoustic impedance of the reference substance, St is the
reflected signal after Fourier transform, and Sr is the reference
signal after Fourier transform.
[0062] The obtained acoustic impedance may be converted into other
dynamic properties such as volume elasticity. By converting the
acoustic impedance and the dynamic property after conversion into
images, it is possible to visually recognize the irregular state
and elasticity of the skin surface.
[0063] FIG. 7 is a flowchart of the surface property measurement
method according to the embodiment. First, the reference signal Sr
representing the component reflected from the reference substance
and the acoustic impedance thereof are acquired in advance (step
S101). The reference signal Sr reflected from the reference
substance and the acoustic impedance thereof are stored in the
memory 33. As the reference substance, other than the
above-described couplant 10, water and gel, etc., may be used. The
reflected signal (reference signal) Sr from the reference substance
is the value after the Fourier transform.
[0064] Furthermore, the reflected signal St from the measurement
target is acquired (step S102). This reflected signal St is also a
value after Fourier transform. Next, the maximum value Rm of the
cross-correlation function between the reflected signal St and the
reference signal Sr is calculated (step S103).
[0065] By using the measurement result and the calculated Rm, the
reflection component St.sup.(1) at the interface with the acoustic
window 5 is calculated (step S104). It is determined whether the
reflection component St.sup.(1) at the interface is lower than the
reference signal Sr (step S105). If the reflection component
St.sup.(1) at the interface is lower than the reference signal Sr
(YES in step S105), it means that the acoustic window 5 is actually
in contact with the measurement target. In this case, the acoustic
impedance of the measurement target is calculated and output (step
S106).
[0066] When the reflection component St.sup.(1) at the interface is
not lower than the reference signal Sr (NO in step S105), it means
that the acoustic window 5 is in direct contact with the reference
substance. In the case of the skin surface, it means that the
portion corresponding to the skin groove 55 is being measured. In
this case, the acoustic impedance of the reference substance is
output (step S107). Once the acoustic impedance is obtained over a
predetermined range, the surface properties are evaluated (step
S108), and the process is ended.
[0067] By the above method, it is possible to accurately measure
and evaluate fine irregularities and dynamic properties of the
surface, by measuring surface properties using ultrasonic waves.
For example, as the evaluation of the skin surface of a person, the
age by decade of the person to which the skin state corresponds,
can be evaluated, based on the fineness of texture, the smoothness,
and the elasticity, etc.
[0068] FIG. 8 illustrates an ultrasonic image of the living human
skin and the acoustic impedance on a line X-X', when the
cross-correlation between the reflected wave from the target and
the reference wave is not used. The horizontal axis of the image is
the length (.mu.m) and the vertical axis is the acoustic impedance
(Pas/m.sup.3).
[0069] FIG. 9 illustrates an ultrasonic image and the acoustic
impedance on the line X-X' when applying the technique of the
above-described embodiment to the same sample as that of FIG.
8.
[0070] Both FIG. 8 and FIG. 9 illustrate acoustic impedance images
of the two-dimensional profile of skin on the forearm inner side
(flexion side) of a healthy 20-year-old male. The skin was measured
after washing and then drying for a certain period of time. For the
measurement, a transducer of 40 MHz to 120 MHz was used, ultrapure
water was used for the couplant, and an acrylic plate was used for
the substrate with which the skin was brought into contact.
Focusing on the wavelength most reflected by the surface, images
were acquired at 200.times.200 pixels.
[0071] In the conventional method illustrated in FIG. 8,
reflections from the inner layers show as interference at the
points A and B on the line X-X', resulting in low values. On the
other hand, in the method of FIG. 9, the reflection components from
the inside were removed and the value of only the horny cell layer
51 was calculated. As described above, by the method according to
the embodiment, the surface irregularity information can be
accurately acquired.
[0072] FIG. 10 illustrates a process flow when the acquired
acoustic impedance is displayed as image information. This process
can also be performed by the DSP 34 or the CPU 31 of the
information processing apparatus 3. The same steps as those in FIG.
7 are denoted by the same reference numerals. First, a reflected
signal (Fourier transformed signal) Sr from the reference substance
and the acoustic impedance thereof are acquired in advance (step
S101). Coordinate data of measurement points at the time of
relatively scanning the ultrasonic waves with respect to the
measurement target, is acquired (step S201). In the relative
scanning, the probe 2 may be scanned with respect to a fixed
measurement target, or the ultrasonic sensor circuit 21 may be
fixed and a stage holding the sample may be two-dimensionally
driven.
[0073] Next, the acoustic impedance at each measurement point is
acquired (step S202). The acoustic impedance of the target or the
acoustic impedance of the reference substance is acquired by
comparing the interface reflection intensity and the reference
signal intensity based on the maximum cross-correlation function
between the Fourier-transformed reference signal and the reflected
signal from the target, as in S102 to S107 in FIG. 7. Image data is
generated with gradation or color according to the acoustic
impedance (step S203).
[0074] It is determined whether there are other measurement points
(step S204). If there is another measurement point (YES in S204),
steps S201 to S203 are repeated. Upon completion of the processes
of steps S201 to S203 for all measurement points (YES in S204), the
image is displayed (step S205).
[0075] In the above flow, once the reflected wave and the Fourier
transform value thereof are stored in association with the
coordinate value in the memory 33 for all of the measurement
points, the acoustic impedance at each coordinate point may be
calculated. In this case also, if image data is generated for all
coordinate points, the image is displayed on the display device 36.
Furthermore, the acoustic impedance may be converted into another
dynamic property and displayed in gradation or color according to
the conversion value.
[0076] According to the above method, it is possible to accurately
measure the surface properties by distinguishing between the horny
cell layer 51 actually contacting the acoustic window 5 and the
portion corresponding to the skin groove 55, and excluding the
reflection components from the inner layer.
[0077] FIGS. 11A to 11D are images illustrating the state of the
skin surface actually measured by using the surface property
measurement apparatus 1 according to the embodiment. The skin
surfaces of the cheeks of 70 females in their 20 s to 80 s were
measured. The breakdown of the 70 females was 19 females in their
20 s (20-29 years old), 15 females in their 40 s (40-49 years old),
19 females in their 60 s (60-69 years old), and 17 females in their
70 s and 80 s (70-86 years old).
[0078] As a measurement method, this time, in order to eliminate
the influence of the movement of the body and to obtain a more
accurate value, the probe 2 was fixed vertically such that the
acoustic window 5 was horizontal. The probe 2 was arranged such
that the cheek of the measured person horizontally contacts the
acoustic window 5, the leading end of the probe 2 of the surface
property measurement apparatus 1 was pressed against the cheek,
ultrasonic waves were radiated onto the skin of the measurement
target region, the reflected signals from the measurement target
region were acquired, and the acoustic impedance was calculated.
The acoustic window 5 of the probe 2 was formed of acrylic having a
thickness of 0.5 mm. Physiological saline was applied as a couplant
to the measured person's cheek in advance. The measurement was
carried out under constant conditions of a humidity of 45% and a
temperature of 25.degree. C.
[0079] FIGS. 11A to 11D illustrate the results of selecting a
representative example of an acoustic impedance distribution of
each measurement group (20 s, 40 s, 60 s, and 80 s). The portions
with high acoustic impedance (the white portions and the
light-color portions) in the image are skin, the portions with low
acoustic impedance (the black portions and the dark-color portions)
in the image bubbles and couplant. The reflected signals from the
measurement region were cross-correlated with previously acquired
reference reflected signals of the reference substance
(physiological saline), and the reflection component at the
interface was calculated with the maximum value of the
cross-correlation function as an index, to calculate the acoustic
impedance. The calculated acoustic impedance indicates an accurate
measurement result from which the interference component caused by
internal reflection has been removed.
[0080] It can be seen that as age increases, the impedance in the
image turns white (high impedance). In the skin of the females in
their 20 s in FIG. 11A, the impedance distribution is uniform
overall. This indicates that the hillocks rise equally with
elasticity and the texture is fine. In FIG. 11B to FIG. 11D, as age
increases as the 40 s, the 60 s, and the 80 s, the high-impedance
portions increase. This is considered to be due to the thickening
of the horny cell layer and the roughening of the texture with
aging. Furthermore, locally low impedance portions exist in the
skin of the 40 s and the 60 s because the acoustic impedance is low
as the couplant enters wrinkles and cracks due to the thickening of
the horny cell layer. In this way, from the measurement result of
the skin surface using the acoustic impedance, not only is it
possible to obtain the accurate acoustic impedance value of the
horny cell layer excluding the influence of irregularities and the
influence inside the skin, but it is also possible to obtain
information regarding on the fineness and smoothness of the
skin.
[0081] FIG. 12 illustrates the average acoustic impedance by age
based on the measurement results of FIGS. 11A to 11D. Among the
four groups, the average acoustic impedance of 20 s (20 to 29 years
old) is indicated at age "20". The average acoustic impedance of
the 40 s (40 to 49 years old) is indicated at age "40". The average
acoustic impedance of 60 s (60-69 years old) is indicated at age
"60". The acoustic impedance of the 70 s and the 80 s (70-86 years
old) is the age "80". As age increases, the acoustic impedance
tends to be higher, and the relationship between aging and the
hardening of the horny cell layer can be inferred.
[0082] As illustrated in FIGS. 11A to 11D, by acquiring the average
acoustic impedance distribution for each age group in advance, the
skin age of the measured person can be estimated. The skin age may
or may not match the actual age. If the measured skin age is higher
than the actual age, measures can be recommended according to the
degree of the difference.
[0083] As described above, by using the configuration and the
technique of surface property measurement according to the
embodiment, surface properties can be evaluated (step S108 in FIG.
7) with increased accuracy.
[0084] When the above method is implemented by the surface property
measurement program, the surface property measurement program is
stored in advance in the memory 33 or the storage device 37, and
the CPU 31 reads out the surface property measurement program and
executes the surface property measurement program.
[0085] The surface property measurement program causes the CPU 31
to execute
[0086] (a) a procedure of acquiring a reflected signal of an
ultrasonic wave radiated to a measurement target;
[0087] (b) a procedure of calculating a maximum value of a
cross-correlation function between the reflected signal from the
measurement target and a reference reflected signal from a
reference substance acquired in advance;
[0088] (c) a procedure of calculating a reflection component at an
interface of the measurement target, by using the maximum value of
the cross-correlation function; and
[0089] (d) a procedure of outputting, as a measurement value, one
of an acoustic impedance of the measurement target or an acoustic
impedance of the reference substance, according to a result of
comparing the reflection component with the reference reflected
signal. Accordingly, a surface property can be evaluated with high
accuracy.
[0090] The present international patent application claims the
benefit of priority of Japanese Priority Patent Application No.
2015-192075, filed on Sep. 29, 2015 to the Japanese patent office,
and Japanese Priority Patent Application No. 2016-175317, filed on
Sep. 8, 2016 to the Japanese patent office, the contents of which
are incorporated herein by reference in their entirety.
INDUSTRIAL APPLICABILITY
[0091] According to the present invention, the hardness information
of the surface of a specimen or a sample can be measured with high
accuracy, and therefore the present invention can be used for
evaluating the dynamic properties of the living body surface such
as the skin, hair, nails, and teeth, and the physical properties
and the presence or absence of defects of an organic or inorganic
surface and/or surface layer.
REFERENCE SIGNS LIST
[0092] 1 surface property measurement apparatus [0093] 2 probe
[0094] 3 information processing apparatus [0095] 5 acoustic window
[0096] 21 ultrasonic sensor circuit [0097] 31 CPU (processor)
[0098] 33 memory [0099] 34 DSP (signal processing unit) [0100] 37
storage device
* * * * *